Systems and methods of generating electricity using heat from within the earth

ABSTRACT

Systems and methods for producing energy from a geothermal formation. A heat exchanger can be disposed within a well to absorb heat from a geothermal formation. The heat exchanger can be supported within the well using a high thermal conductivity material. The heat exchanger is connected to an organic Rankine cycle engine including a secondary heat exchanger and a turbine. The primary and secondary heat transfer fluids are chosen to maximize efficiency of the organic Rankine cycle.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Conventional systems for generating electricity for consumption and useby the public include nuclear power, fossil fuel powered steamgeneration plants and hydroelectric power. Operation and maintenance ofthese systems is expensive and utilizes significant natural resources,and in some cases results in excessive pollution, either throughhydrocarbon combustion or spent nuclear fuel rod disposal. Furthermore,even renewable energy resources such as solar and wind powered systemsare only operational for an average of only a few hours per day in somelocations while geothermal systems can operate on approximately a 24/7basis as required.

Therefore, there is a need in the art for systems and methods forgenerating clean electrical power cheaply which is available on anapproximate 24/7 basis without relying upon the import of petroleummaterials or building of multi-billion-dollar power plants. There isfurther a need for systems and methods for generating electricity usingheat from within the earth.

SUMMARY

In one aspect described herein, a geothermal energy system comprises aprimary heat exchanger positioned within a well, the well in contactwith a geothermal feature and a heat carrier within the geothermalformation, the primary heat exchanger containing a first heat transferfluid configured to absorb heat from the heat carrier in the primaryheat exchanger; a secondary heat exchanger in thermal communication withthe primary heat exchanger, the secondary heat exchanger containing asecond heat transfer fluid, wherein the first heat transfer fluid andthe second heat transfer fluid are maintained separate from each other,and wherein the second heat transfer fluid has a flash point below thatof water; and a turbine in fluid communication with the secondary heatexchanger, wherein the second heat transfer fluid is vaporized in thesecondary heat exchanger and the vaporized second heat transfer fluid isthe working fluid in the turbine; and a generator connected to theturbine, the generator configured to generate electricity based onmovement of the turbine.

In some embodiments, the primary heat exchanger comprises a supplyportion and a return portion, the supply portion comprising a shell inthermal communication with the geothermal feature, and wherein thereturn portion is concentrically located within the shell of the supplyportion.

In some embodiments, the return portion comprises a thermally insulatedpipe, wherein the thermally insulated pipe is configured to insulate thehot first heat transfer fluid in the return portion from the relativelycolder first heat transfer fluid in the supply portion of the primaryheat exchanger.

In some embodiments, the thermally insulated pipe is suspended withinthe shell of the primary heat exchanger via a plurality of centralizers,the centralizers positioned within the shell of the primary heatexchanger such that the primary heat exchange fluid is in contact withthe plurality of centralizers.

In some embodiments, the plurality of centralizers are connected to anouter surface of the thermally insulated pipe and are not connected toan inner surface of the shell.

In some embodiments, the thermally insulated return pipe has a first endlocated near a bottom portion of shell of the supply portion and asecond end connected to the secondary heat exchanger, and wherein thefirst end of the thermally insulated return pipe is closed and comprisesa plurality of perforations therein to allow the first heat transferfluid to flow from the supply portion into the thermally insulatedreturn pipe.

In some embodiments, the shell comprises a well casing, the casingcomprising a plurality of casing segments positioned within the well.

In some embodiments, the plurality of centralizers are connected to aninner surface of the casing at junctions between the casing segments.

In some embodiments, the primary heat exchanger is supported within thewell by a cement or grout having high thermal conductivity.

In some embodiments, the primary heat exchanger is supported within thewell by a plurality of support collars.

In some embodiments, the primary heat exchanger is suspended at or nearthe surface of the earth or the sea floor.

In some embodiments, the heat carrier comprises a thermally conductivematerial inserted between an outer surface of the primary heat exchangerand an inner surface of the wall.

In some embodiments, the heat carrier is a brine flowable within thegeothermal formation.

In some embodiments, each of the plurality of support collars comprise afirst and second end, wherein the first ends of the plurality of supportcollars are securely connected to an inner wall of the well, and whereinthe second ends of the plurality of support collars contact an outershell of the primary heat exchanger plurality at a point higher in thewell than the corresponding first ends of the plurality of supportcollars.

In some embodiments, the plurality of support collars support the outershell of the primary heat exchanger at a position above the bottom ofthe well.

In some embodiments, the plurality of support collars are positionedwithin the well such that the plurality of support collars are incontact with the heat carrier in the geothermal formation, and the heatcarrier is able to flow around the plurality of support collars tocontact the primary heat exchanger.

In some embodiments, the shell comprises an anti-scaling coating on awell-facing surface of the shell, the coating comprising a very smoothnon-metallic material which prevents an ionic bonding site from forming,thus preventing scale formation and also inhibiting corrosion.

In some embodiments, the shell comprises an anti-scaling coating on awell-facing surface of the shell, the coating comprising a non-metalmaterial, such as carbon or boron applied via chemical vapor depositionor vapor deposition alloying.

In some embodiments, the shell comprises an anti-scaling coating on awell-facing surface of the shell, the coating comprising an amorphouscarbon material that has significant amounts of sp3 hybridized carbon toretard both corrosion and scaling.

In some embodiments, the shell comprises an anti-scaling coating on awell-facing surface of the shell, the coating comprising carbon nitride,boron nitride, to prevent or minimize scaling and corrosion.

In some embodiments, the shell comprises an anti-scaling coating on awell-facing surface of the shell, the coating comprising highlythermally conductive ceramics which resist scaling and corrosion

In some embodiments, the first heat transfer fluid is a nanofluid.

In another aspect described herein, a method of generating electricityusing geothermal energy comprises moving a first heat transfer fluidinto a primary heat exchanger positioned within a well, the well incontact with a geothermal feature and a heat carrier within thegeothermal formation; absorbing, in the first heat transfer fluid, heatfrom the heat carrier in the well; moving the first heat transfer fluidout of the primary heat exchanger and out of the well and into asecondary heat exchanger; transferring heat from the first heat transferfluid to the second heat transfer fluid within the secondary heatexchanger, vaporizing the secondary heat transfer fluid in the secondaryheat exchanger; flowing the vaporized secondary heat transfer fluid intoa turbine, the turbine connected to an electrical generator and thevaporized secondary heat transfer fluid moving the turbine; andgenerating electricity in the electrical generator using the movement ofthe turbine.

In some embodiments, moving the first heat transfer fluid into theprimary heat exchanger comprise moving the first heat transfer fluiddown a supply portion of the primary heat exchanger; and contacting,with the first heat transfer fluid, a shell of the primary heatexchanger and a surface of a return pipe disposed concentrically withinthe shell of the primary heat exchanger.

In some embodiments, moving the first heat transfer fluid out of theprimary heat exchanger and out of the well comprises flowing the primaryheat transfer fluid through a return pipe disposed concentrically withina shell of a supply portion of the primary heat exchanger, wherein thereturn pipe is thermally insulated to minimize heat transfer between theprimary heat transfer fluid within the return pipe and the primary heattransfer fluid in the supply portion of the primary heat exchanger.

In some embodiments, the primary heat exchanger within the well issupported via a thermal cement or grout having high thermalconductivity.

In some embodiments, the primary heat exchanger is supported within thewell via a plurality of support collars.

In some embodiments, the method further comprises flowing the heatcarrier between an inner surface of the well and the outer surface ofthe primary heat exchanger, and around the plurality of support collars.

In some embodiments, the method further comprises inserting the primaryheat exchanger into the well, the primary heat exchanger having aplurality of support collars attached thereto, the first end of each ofthe plurality of support collars being moveably attached to an outersurface of the primary heat exchanger, and a second end of each of theplurality of support collars being temporarily connected to the outersurface of the primary heat exchanger via a degrading connection; anddegrading the temporary connection such that the second end of each ofthe plurality of support collars extends to contact an inner surface ofthe well.

In some embodiments, the well comprises a casing extending only along aportion of the well, and the method further comprises drilling, using anunder reamer, a portion of the well where the casing does not extend toincrease the diameter of the well; and positioning the primary heatexchanger in the portion of the well having the increased diameter.

In another aspect described herein, a heat exchanger for use in ageothermal application comprises a casing disposed within a well, havingan anti-scaling and/or anti-corrosion layer thereon configured tocontain a heat transfer fluid, the casing forming a shell to hold a heattransfer fluid; a plurality of support collars disposed within the well,the plurality of support collars supporting the casing within the well,the plurality of support collars disposed at a generally upward anglefrom an inner surface of the well toward the casing; a return pipedisposed co-axially within the cylindrical shell, wherein thearrangement of the casing and the return pipe form an annulus betweenthe return pipe and the cylindrical shell, the inner volume of thereturn pipe being thermally insulated from the annulus; a plurality ofcentralizers disposed within the annulus, each of the plurality ofcentralizers comprising a first end and a second end, the first end ofthe plurality of centralizers connected to an inner surface of the shelland the second ends of the plurality of centralizers connected to anouter surface of the return pipe, the centralizers having a low profileto minimize hydraulic resistance to flow within the annulus; and whereinthe plurality of support collars are configured to allow flow of a heatcarrier between the inner surface of the well and the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the Seebeck Effect for thermoelectricsystems according to an exemplary embodiment.

FIG. 2 illustrates a thermopile of the thermoelectric system accordingto an exemplary embodiment.

FIG. 3 illustrates a thermoelectric generator according to an exemplaryembodiment.

FIG. 4 is an illustration of a thermoelectric generation systemaccording to an exemplary embodiment.

FIG. 5 is an illustration of temperatures within the earth's surfaceaccording to an exemplary embodiment.

FIG. 6 is an illustration of an exemplary pipe structure including aninterior pipe and an exterior pipe according to an exemplary embodiment.

FIG. 7 is an illustration of a thermoelectric generation systemaccording to an exemplary embodiment.

FIG. 8 is an illustration of a thermoelectric generation systemaccording to an exemplary embodiment.

FIGS. 9A and 9B is an illustration of a pipe system according to anexemplary embodiment.

FIG. 10 is an illustration of a thermoelectric generation systemaccording to an exemplary embodiment.

FIG. 11 is an illustration of a thermoelectric generation systemaccording to an exemplary embodiment.

FIG. 12A is a system diagram of an embodiment of a geothermal energyproduction system.

FIG. 12B is a cutaway view of an embodiment of a heat exchanger within awell.

FIG. 12C is a cutaway view of an embodiment of a heat exchanger within awell.

FIG. 12D is a top view of a portion of a heat exchanger.

DETAILED DESCRIPTION

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which an exemplary embodimentof the invention is shown. This application may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, this embodiment is provided sothat this disclosure will be thorough and will fully convey the scope ofthe invention to those skilled in the art. Like numbers refer to likeelements throughout.

Some embodiments of the current disclosure utilize deep wells (forexample, abandoned or non-utilized oil, gas and geothermal wells) whichcan be obtained for very little investment and fit them with a mediumrecirculation type system to provide sufficient heat energy forelectrical power generation, direct heating and/or water condensation.For example, the power generation means may include thermoelectricgenerators, Stirling engines, Rankine engines, Matteran energy cycleengines, flash power plants, dry steam power plants, binary organicRankine cycle power plants, flash/binary combined cycles, and the like.The deep wells may generate heat energy while a separate lowertemperature source may provide a cold source for creating a temperaturedifferential, a heat sink, or the like, as is used by the various powergeneration means described herein. For example, the separate lowertemperature source may be provided by water obtained from a variety ofsources including an ocean, sea, gulf, river, stream, creek, lake,spring, or from any underground source such as underground wells or frompublic water systems. The power generation means may be used to providepower for public, private and government consumption.

Methods and systems of the current disclosure have many inherentadvantages resulting from the efficient design that takes advantage ofavailable energy sources and which limits the physical and ecologicalfootprint and waste resulting from its use. For example, designed as aclosed loop or substantially closed loop process, some disclosedembodiments can reduce pollution and unnecessary introduction ofnon-natural materials to the surrounding environment when in use,including into the earth's surface, underground, and into the earth'satmosphere. Furthermore, the closed loop nature and the reliance onexisting energy sources reduces the creation of additional waste orundesirable byproducts as are often generated with current geothermalenergy generation systems. Through the use of heat energy alreadyexisting within the earth, embodiments of the invention may additionallyprovide an untapped alternative energy source, overcoming many of thefuel dependency problems currently faced. Embodiments of the inventionmay also be scalable through the inclusion of multiple energy generationmeans and multiple heat sources, providing an alternate energy sourcefor local use and/or for contributing to larger private or public grids.Additionally, scalability may be achieved through economically prudentsystem construction, avoiding excessive construction costs, time, andspace. Finally, embodiments of the invention create an opportunity toleverage existing energy already accessible via non-producing wells,such as spent wells or exploration wells, that otherwise may be unusedor under-utilized.

A first example embodiment described herein may include a thermoelectricgenerator comprising a thermopile, a hot junction, and a cold junction.The hot junction of the thermopile may be coupled to a high temperaturesource comprising heat from within the earth's surface. Additionally,the cold junction of the thermopile may be coupled to a low temperaturesource from a body of water, which may be geographically separated fromthe cold junction. The high temperature source and the low temperaturesource thus may create a temperature gradient at the thermopile forgenerating electricity.

As illustrated in FIG. 1 continuously flowing electrical current may becreated when a first wire 12 of a first material is joined with a secondwire 14 of a second material and then heated at one of the junction ends16. This is known as the Seebeck Effect. The Seebeck effect has two mainapplications: temperature measurement (thermocouple) and powergeneration. A thermoelectric system is one that operates on a circuitthat incorporates both thermal and electrical effects to convert heatenergy into electrical energy or electrical energy to a decreasingtemperature gradient. The combination of the two or more wires creates athermopile 10 that is integrated into a thermoelectric system. Whenemployed for the purposes of power generation, the voltage generated isa function of the temperature difference and the materials of the twowires used. A thermoelectric generator has a power cycle closely relatedto a heat engine cycle with electrons serving as the working fluid andcan be employed as power generators. Heat is transferred from a hightemperature source to a hot junction and then rejected to a lowtemperature sink from a cold junction or directly to the atmosphere. Atemperature gradient between the temperatures of the hot junction andthe cold junction generates a voltage potential and the generation ofelectrical power. Semiconductors may be used to significantly increasethe voltage output of thermoelectric generators.

FIG. 2 illustrates a thermopile 20 constructed with a n-typesemiconductor material 22 and a p-type semiconductor material 24. Forincreased electrical current, the n-type materials 22 are heavily dopedto create excess electrons, while p-type materials 24 are used to createa deficiency of electrons.

Thermoelectric generator technology is a functional, viable andcontinuous long-term electrical power source. Due to the accessibilityof temperature gradients occurring in natural and man-made environments,thermoelectric generators can provide a continuous power supply in theform of electricity. One of the most abundant, common, and accessiblesources of energy is environmental heat, especially heat containedwithin the earth's crust.

FIG. 3 illustrates an embodiment of the thermoelectric generator. Thethermoelectric generator 300 may include an input 310 to a plurality ofhot junctions 320 and an output 330 to the plurality of hot junctions320. The hot junctions 320 may include any source of heat for heattransfer. In an exemplary embodiment, the source of heat is a hot plate332. The hot plate 332 may be metal or any other conductive material.The hot plate 332 may interface the thermopile 350 to provide heat tothe thermopile through conduction, convection, radiation, or any otherheat transfer means. One of ordinary skill in the art will appreciatethat any thermoelectric generator may be used herein and is not limitedto this embodiment. Any system that allows the heat to access thethermopile is contemplated herein.

The thermoelectric generator 300 may further include a plurality of coldjunctions 360. The cold junctions 360 may include a cold plate 312 forheat transfer. Alternatively, heat may be radiated or convected awayfrom the cold junctions 360. The cold plate 312 may be metal or anyother conductive material. The cold plate 312 may interface thethermopile 350 to provide a conductive heat sink. Voltage potential maybe created across the thermopile 350 from a temperature gradient betweenthe temperature of the hot plate 332 and the temperature of the coldplate 312. The greater the temperature gradient, the more electricalpower may be generated. One of ordinary skill in the art will appreciatethat any thermoelectric generator may be used herein and is not limitedto this embodiment.

Any system that provides a heat sink that interfaces thermopile iscontemplated herein, including naturally occurring sources of heatabsorption such as a fluid. In an exemplary embodiment, the fluid iswater. Water may be obtained from any source including an ocean, sea,gulf, river, stream, creek, lake, spring, or from any underground sourcesuch as underground wells or from public water systems for the purposesof this application. Since the water is used to absorb heat, water froma public water system used as the heat sink herein may serve anancillary purpose of preheating the water to decrease the power requiredby the public, government, or industry to heat the water for any desireduse. Water or any fluid as the low temperature source provides atechnical benefit over air or gas by having a higher heat transfercoefficient and therefore providing better heat transfer with the coldjunction.

FIG. 4 illustrates an exemplary embodiment of a thermoelectricgeneration system 400. A thermoelectric generator may be used in thethermoelectric generation system to produce electrical power from atemperature gradient between a low temperature source and a hightemperature source. The thermoelectric generation system 400 may belocated in or near a body of water 402 including but not limited to anocean, gulf, sea, lake, river, spring, creek, or any other relativelycooler body of water. The thermoelectric generation system 400 utilizesthe body of water 402 as the low temperature source for thethermoelectric generator.

The body of water 402 can provide significantly lower temperatures tothe thermoelectric generator to increase the temperature gradient. In abody of water 402, such as an ocean, gulf, sea, or lake, the temperatureof the water decreases with depth. At a depth commonly referred to asthe thermocline, the water temperature significantly decreases. Thedepth at which a thermocline occurs averages between 30 and 50 meters,and varies throughout the world. It is preferred for the low temperaturesource to be water at a depth below the thermocline to provide acontinuous source of cold water, and preferably in a current to allow acontinuous flow of cool water so that the water is not stagnant andtherefore rises in temperature throughout energy production operations.Additionally, location of the power plant adjacent to some other surfacebody of relatively cooler water will allow the water to flow through theplant and then be discharged with minimal thermal change of the water.

Accordingly, the low temperature source may either be in direct contactwith the cold junction, or alternatively may be geographically separatedfrom the cold junction and fluidly communicate by a pipe or other meansof medium transport.

The high temperature source may be provided from within the earth'scrust 404. The earth provides a continuous, inexpensive source ofextremely high heat. As illustrated in FIG. 5, the temperature withinthe earth generally increases towards the core of the earth at anaverage rate of approximately 1 degree Fahrenheit for every 60 feet ofdepth. Therefore, locations deep within the earth may be used as thehigh temperature source for the hot junction of the thermoelectricgenerator. Locations within the earth may be accessed through drillingor other means for creating a hole 416 in the ground and water or someother type of heat transfer medium circulated through the hole andbrought to or near the surface to allow for heat transfer to occur bythe employment of high efficiency pumps or some other method.

Certain holes, commonly referred to as dry holes may be used to accessthe high temperatures within the earth's crust. Dry holes typicallyexist from the unsuccessful efforts of the petroleum industry to locateoil or gas. The petroleum industry drills wells deep into the earth'scrust for the exploration for petroleum. The overwhelming majority ofexploration wells drilled throughout the world do not locate petroleumand are thereby indicated as “dry holes.” Dry holes provide relativelyeasy access to the subterranean levels and high temperature conditions.Dry holes may be located on land or in a body of water. Dry holes mayreach depths in excess of 30,000 feet. However, one of ordinary skill inthe art will appreciate that dry holes may be any depth and can beeither active or inactive functioning or non-functioning oil, gas and/orgeothermal wells.

FIG. 5 shows the relationship between temperature and depth in theearth's crust for an exemplary well. As shown in FIG. 5, temperatures inthe wells or dry holes can reach very high temperatures. In theexemplary depiction in FIG. 5, temperatures in a dry well areapproximately 209° F. at 6100 feet. One of ordinary skill in the artwill appreciate that the present disclosure is not limited to the use ofdry holes and may include any hole or well in the earth's crust whichcan provide a heat source including holes drilled for use by athermoelectric generator as well as expended or unused oil and gaswells. FIG. 5 is exemplary for one well. In some wells temperatureprofiles can vary, and down hole temperatures can be greater than 209°F. at 6100 feet.

Referring again to FIG. 4, the thermoelectric generation system mayinclude a pump station 410, a pipe system 420, a thermoelectricgenerator 430, and a heat transfer fluid 440. The thermoelectricgeneration system may be positioned in or proximate to a body of water402. The pump station 410 may include a pump and associated housing forthe pump. The pump may be any commercially available or speciallydesigned pump that is capable of forcing fluid to flow at a suitablevolumetric rate. The pump station 410 may be located on land, above thewater surface, or underneath the water. The pump station 410 isconnected to the pipe system 420. The pipe system 420 includes at leastone pipe 422. The pipe 422 may include an inner bore or inner channelfor carrying fluid heat transfer 440 to be heated by the earth. Theinner bore may be any suitable diameter that allows sufficient heattransfer fluid 440 to be pumped through the pipe system. The pipe 422extends from the pump station 410 into the hole 416 and may besubstantially U-shaped such that the pipe 422 ascends out of the hole.

The pipe system 420 may interface a hot junction 320 of thethermoelectric generator 430. The inner bore of the pipe 422 of the pipesystem 420 is accessible to an input of the hot junction 320 of thethermoelectric generator 430. The pipe system 420 extends from an outputof the hot junction 320 of the thermoelectric generator 430 to return tothe pump station 410.

Accordingly, the pipe system 420 may be configured in a closed loop or asubstantially closed loop configuration between the pump station 410 andthe thermoelectric generator 430. More specifically, the heat transfermedium being pumped from the pump station 410 into the high temperaturesource existing under the earth's surface (for example, within anexisting well) and back to the surface to the hot junction 320 of thethermoelectric generator may never become exposed to the surroundingelements within and be entirely contained in the pipe system 420 untilits interface at the hot junction. However, it is appreciated that itmay be necessary to add, replace, or replenish the heat transfer mediumat the pump station 410.

In some embodiments, the pump station 410 provides a positive pressureto a first portion of the pipe system 420 and pumps the heat transferfluid 440 downward from the surface into the hole 416, where the fluidabsorbs heat from the geological formation. The heat transfer fluid 440then flows upward through the inner bore of the pipe 422 to thethermoelectric generator 430, where the heat transfer fluid 440 gives upheat to the thermoelectric generator 430. The heat transfer fluid 440then recirculates through the pump station 410, and is again forceddownward, and the cycle repeats.

In some embodiments, the pumping station 410 provides a suction orvacuum force on the pipe system 420, thereby drawing fluid from aportion of the pipe system 420, such as from the portion of the pipesystem 420 in thermal communication with the thermoelectric generator430. The heat transfer fluid 440 then gravity drains, or, as desired, isdrawn downward into the hole to circulate.

In an exemplary embodiment illustrated in FIG. 6, the pipe system mayinclude an exterior pipe 423 and an interior pipe 424 such that anannulus 425 exists between the interior pipe 424 and the exterior pipe423. In this exemplary embodiment, the fluid 440 may be pumped into thehole through the interior pipe 424, and the fluid 440 heated by theearth may be pumped out the hole 416 through the annulus 425 to the hotjunction 320 of the thermoelectric generator 430.

In some embodiments, the fluid 440 to be pumped into the hole throughthe annulus 425 and pumped out of the hole through the interior pipe424. It is appreciated that, depending upon the surrounding environmentand temperatures that the pipe system 420 will be interfacing, thereturning fluid pumped down-ward through the annulus 425 mayadditionally insulate the heated medium pumped up through the interiorpipe 424.

In another embodiment of the thermoelectric generation systemillustrated in FIG. 7, the hole 416 may be located on the land proximateto a body of water. The hole 416 may provide the high temperature sourcefor the hot junction as described previously. The body of water 402 mayprovide the low temperature source for the cold junction. The body ofwater 402 may be a river, spring, creek, lake, or any other cold watersupply. The cold junction 360 of the thermoelectric generator 430 isthermally coupled to the body of water 402. The cold junction 360 mayinterface directly with the body of water 402 or the body of water maybe directed to the cold junction 360 using a pipe 422 of a pipe systemor other means of channeling the water such as a heat exchanger. Thecold junction 360 is cooled to approximately the temperature of thewater interfacing the cold junction. The thermoelectric generator 430creates a voltage potential across the hot junctions 320 and the coldjunctions 360 of the thermoelectric generator 430. The use of the heatfrom the earth to control the temperature of the hot junction 320 andthe coldness of the surface or near surface water to control thetemperature of the cold junction 360 maximizes the temperature gradientand produces significant amounts of electrical power through theemployment of the thermoelectric modules. The electricity generated fromthe thermoelectric generator 430 may transmitted through power lines 450to any destination.

In another embodiment of the thermoelectric generation systemillustrated in FIG. 8, the low temperature source for the cold junction360 may be water from a chiller device 810 residing at, above, or belowthe surface of the earth. Due to the low temperatures immediately belowthe earth's surface, the chiller device 810 may be used to lower thetemperature of the water. In an exemplary embodiment, the chiller devicemay be placed at a depth up to approximately 300 feet below the surface.At approximately 300 feet below the surface, the temperature generallybegins to increase with depth. One of ordinary skill in the art willappreciate that the 300 feet level is only an approximation and that thedepth may vary depending on location on the earth and is therefore notlimited to the 300 feet approximation. The chiller device 810 may bepowered from electricity generated from the thermoelectric generator.

The utilization of water as the medium for heat transfer from deepwithin the earth's crust may cause corrosion of a metal pipe system. Hotwater, especially when containing oxygen, may rapidly corrode metal. Toreduce corrosion, a de-oxygenation mechanism, such as a high vacuum, maybe employed to remove oxygen from the water. Alternatively,non-corrosive metals such stainless steel may be used for the pipesystem. In another embodiment, the pipe system may include hightemperature resistant and non-corrosive plastic piping. An exemplaryembodiment of the plastic piping is piping manufactured from PARMAX®materials. One of ordinary skill in the art will appreciated that anynon-corrosive and temperature resistant plastic may be used. In yetanother embodiment, corrosive preventative substances may be used tominimize corrosion. For example, chromates or other chemicals may beused. As an alternative to water, a non-corrosive fluid such as asynthetic oil or mineral oil or specialty heat transfer fluid may beused to absorb the heat from within the earth's crust for the hightemperature source. Oil has the added advantage of being able to beheated to a higher temperature than water and therefore more power maybe drawn from the thermoelectric generation system in this manner.

The thermoelectric generator can be protected from the low temperaturesource during operation to extend the life of the thermoelectricgenerator. Protection may be in the form of chemical protection or anyother source. The cold junction may include ceramic materials to resistcorrosion from the water. The thermoelectric generator also may besealed such that water does not engage or corrode the thermopiles.

The thermoelectric generator may include off-the-shelf thermopiles. Thethermoelectric generators also may employ specially designedthermopiles, such as Quantum Well Thermoelectric Generators, that willsubstantially increase power generation.

The thermoelectric generator also may employ nanowires to increase theefficiency of the system. The nanowires increases the density of states.The nanowires may be arranged in a substantially parallel array totransport generated electricity. The thermoelectric generator also mayinclude quantum dots to increase the efficiency of the system and lowersthe thermal conductivity of the system.

In another embodiment of the thermoelectric generation system, the hightemperature source for the hot junction may be from a mud pit. Mud fromthe mud pit is used as a drilling fluid for oil well drilling. The mudextends to the bottom of the hole being drilled for oil exploration. Themud is heated from the drilling and the high temperatures from withinthe earth's surface. The hot junction of the thermoelectric generatormay interface the mud pit to access the high temperature of the mud. Thehigh temperature of the mud may be used to increase the change intemperature across the thermopile and to increase electrical generation.

The thermoelectric generation system may have several advantages overconventional systems of power generation. For example, thethermoelectric generation system has minimal pollution concerns due inpart to its operation as a closed loop system and will rely uponminimal, if any, introduction of non-natural materials. Thethermoelectric generation system will have minimal waste and minimalatmospheric emissions. The thermoelectric generation system also iscompletely renewable. The thermoelectric generation system also may bescaled down to a level which can provide power for a local area. Thethermoelectric generation system may be inexpensive to construct andoperate compared to conventional power systems and also may takeadvantage of non-producing oil wells instead of having to cap the wellsthat are non-productive or to drill new holes.

FIGS. 9A and 9B illustrate another exemplary embodiment of a pipe system900 having both an exterior pipe 910 and an interior pipe 920, arrangedconcentrically, as is described above with reference to FIG. 6. Asillustrated by FIG. 9A, the interior pipe 920 includes a plurality offins 930 affixed to the exterior surface of the pipe, and which may runalong at least a portion of the pipe length and extend radially outward.In one example, the fins 930 may run substantially the entire length ofthe pipe. In another example, however, the fins 930 may be affixed tothe interior pipe 920 along a length at or near the distal portion ofthe pipe system 900. The fins 930 may facilitate geothermal heattransfer from the earth to the medium being circulated therethrough, andfurther facilitate heat dissipation within the medium. Thus, in anembodiment of the pipe system 900 including fins only at a distalportion of the pipe system 900 would provide the increased heat transfermechanism at or near where the deepest portion of the pipe system wherethe geothermal energy is the greatest. Alternatively, in another exampleembodiment illustrated by FIG. 9B, the plurality of fins 930 may beaffixed to the exterior pipe 910 and extend to radially toward theinterior pipe 920. It is further appreciated that the fins 930 may beaffixed to both the exterior pipe 910 and the interior pipe 910 andextending therebetween. The fins 930 may be constructed of materialshaving a high thermal conductivity, as are known.

Fins as described may also be employed in embodiments having a pipesystem not including both an interior or exterior pipe, such assubstantially U-shaped pipe system as described with reference to FIG.4. In these embodiments, the fins may be affixed to the interior surfaceof the pipe and extend radially inward, further improving geothermalheat transfer from the earth to the fluid pumped therethrough.

The fluid 440 is forced through the pump using the pump station 410. Thefluid 440 is circulated through the pipe 422, the hot junction 320 ofthe thermoelectric generator 430, and the pump station 410 using thepump. Additional fluid may be added to the pipe system 420 eithercontinuously or when needed by the system to account for any loss offluid during operation of the pipe system and pump station. However, oneof ordinary skill in the art will recognize that other methods ofbringing the heated fluid to or near the surface may be employed.

The fluid 440 within the pipe 422 is heated by the earth as it descendsfrom the pump station 410 towards the bottom of the hole 416. The fluid440 may be heated to approach the temperature of the earth in the hole416. In an exemplary embodiment, the fluid 440 may be heated in excessof 200 degrees Fahrenheit. After the fluid 440 reaches the lowest pointof the pipe 422, the heated fluid then ascends out of the hole 416 andinto the input of the hot junction 320 of the thermoelectric generator430.

The heated fluid in the pipes 422 may be the high temperature source andis thermally coupled to the hot junction 320 of the thermoelectricgenerator 430. The fluid exits the inner bore of the pipe 422 and entersthe input of the hot junction 320 of the thermoelectric generator 430.The fluid 440 then may exit through the output 330 of the hot junction320 of the thermoelectric generator 430 through the inner bore of thepipe 422. The fluid 440 continues to the pump station 410 to close thepumping cycle of the fluid. The pump station may include any pump thatis operable to pump the fluid 440 through the pipe system 420 and thethermoelectric generator 430 at an appropriate volumetric rate.Furthermore, the thermoelectric generation system may operate as eithera closed system or an open system.

The fluid 440 may include any fluid that is capable of being heated bythe earth and capable of retaining a substantial portion of the heat fordelivery to the hot junction of the thermoelectric generator. In anexemplary embodiment, the fluid is water, however, other fluids may beemployed to reduce corrosion and to allow heating well above the boilingpoint of water.

The thermoelectric generator 430 may be located in the body of water 402and in communication with the pipe system 420. The body of water 402 isused as the low temperature source for the cold junction 360 of thethermoelectric generator. In the exemplary embodiment of FIG. 4, thethermoelectric generator 430 is located beneath the thermocline of thebody of water 402 so that the cold junction 360 may access the lowtemperature water below the thermocline. In an exemplary embodiment, thethermoelectric generator 430 may be located in a current stream in thebody of water 402 to access a flow of the water. The body of water 402provides the low temperature source for cold junction 360 of thethermoelectric generator 430. The cold junction 360 may be outwardlyexposed to the water in the body of water 402. The cold junction 360 maybe sufficiently protected to prevent corrosion. The water in the body ofwater 402 also may be channeled into the cold junction 360 of thethermoelectric generator. The cold junction 360 may include an input forreceiving the water and an output for exiting the cold water. The watermay flow through the cold junction 360 to provide the low temperaturesource to the cold junction 360 of the thermoelectric generator.

In an exemplary embodiment, the high temperature source may be between100 degrees Fahrenheit and 600 degrees Fahrenheit and the lowtemperature source may be between approximately 32 and 130 degreesFahrenheit. One of ordinary skill in the art will appreciate that thehigh temperature source and low temperature source are not limited tothese temperature ranges but may be any appropriate temperature ranges.The temperature gradient (ΔT) between the hot junction and the coldjunction may be between 470 and 68 degrees in the exemplary embodiment.One of ordinary skill in the art will appreciate that the temperaturegradient is not limited to this range but may be any temperaturegradient.

The thermoelectric generator 430 creates a voltage potential across thehot junction 320 and the cold junction 360 of the thermoelectricgenerator. The use of the heat from the earth to control the temperatureof the hot junction 320 and the coldness of the water to control thetemperature of the cold junction 360 maximizes the temperature gradientand produces significant amounts of electrical power. The electricalpower may be created as a direct current. The direct current may betransformed to an alternating current. A three-phase current may also becreated. The electricity generated from the thermoelectric generator 430may be transmitted through power lines 450 to any destination. In anexemplary embodiment, existing power transfer facilities and powerconduction lines 450 may provide power to any current or newly createdelectrical grid network.

In another embodiment, the high temperature source may be used inconjunction with a steam powered generator. Fluid may be pumped througha pipe system into the earth's crust. The fluid may then be heated bythe earth's crust and pumped to the surface. Using the high temperaturesource to heat the fluid may minimize the power required to operate asteam powered generator by preheating the water to the steam plants. Thecost of heating the fluid to its boiling point, therefore, will besignificantly reduced at hydrocarbon powered or other types ofelectrical plants if the fluid can be brought to a higher temperature asa result of heating within the earth's crust. For example, if the fluidis water, the high temperature source may heat the water to or near itsboiling point. The water then could be converted to steam for use in thesteam power generator. If the fluid is a fluid such as oil that has aboiling point greater than water, the fluid can be heated above 212degrees Fahrenheit such that it can transfer heat through a heatexchanger to water in the steam powered generator to be converted tosteam without the need of any or very little fossil fuels or otherenergy sources. The steam powered generator may be used in conjunctionwith the thermoelectric generation system or completely separatetherefrom.

In some embodiments, the invention may include alternative powergenerating means, instead of a thermoelectric generator, as describedabove. For example, the alternative power generating means may includeStirling engines, Rankine engines, Matteran energy cycle engines, flashpower plants, dry steam power plants, binary power plants, flash/binarycombined cycles, and the like. By way of illustration, Sterling enginesare described as an illustrative embodiment; though it is appreciatedthat the power generation system may include other power generationmeans, such as, Rankine engines, Matteran energy cycle engines, flashpower plants, dry steam power plants, binary power plants, flash/binarycombined cycles, and the like.

A Stirling engine is a heat engine that is vastly different from typicalinternal combustion engines, and can be much more efficient than agasoline or diesel engine. Today, however, Stirling engine use istypically limited to specialized applications, such as in submarines oras auxiliary power generators for yachts, where quiet operation isimportant. A Stirling engine uses the Stirling cycle, which is unlikethe cycles used in internal combustion engines, operating under theprinciples of the Carnot cycle. Example Stirling engines may include analpha-type or beta-type Stirling engine using a single displacer piston,or a gamma-type Stirling engine using at least a two-pistonconfiguration. The gasses used inside a Stirling engine do not escapethe engine. There are no exhaust valves that vent high-pressure gasses,as in a gasoline or diesel engine, and combustion does not occur.Because of this, Stirling engines are very quiet.

An exemplary embodiment of a Stirling engine may include a cylindricalhot chamber with a piston, a cylindrical cold chamber with a piston, agas, and a connecting pipe. A high temperature source may be applied orthermally coupled to the hot chamber to increase the temperature of thegas within the hot chamber. Heat from the high temperature source may betransferred to the gas through conduction, convection, radiation or anyother means. A low temperature source may be applied or thermallycoupled to the cold chamber to decrease the temperature of the gaswithin the cold chamber. Heat from the gas may be extracted by the coldtemperature source through conduction, convection, radiation or anyother means.

As known by those of ordinary skill in the art, the Stirling engineoperates by pressurizing and depressurizing the gas through theapplication of a high temperature source to the hot chamber andapplication of a low temperature source to the cold chamber. Theefficiency and power generated by the Stirling engine also may beincreased through the use of an increased high temperature source and adecreased low temperature source to create a substantial temperaturegradient across the hot chamber and the cold chamber. The temperaturegradient across the hot and cold chambers will increase the pressuredistribution across the engine which causes the pistons, to moreactively move. Thus, the greater the temperature difference between thehot and cold heat exchangers, the more efficient the Stirling engineoperates. The pistons, may be connected to a shaft such that themovement of the pistons causes the shaft to rotate. An electricgenerator may be attached to the shaft to convert the mechanical energyof the rotating shaft to electricity.

An example embodiment of a system employing a Stirling engine isillustrated in FIG. 10. The Stirling engine generation system mayinclude a pump station 1010, a Stirling engine generator 1030 (which asreferred to herein includes both a Stirling engine and an electricalgenerator for the generation of electricity), a pipe system 1020 placedwithin a deep well or other hole 1040 in the earth's crust, and a heattransfer medium flowing through the pipe system 1020, in much the samemanner as described with reference to FIGS. 4-9 and the embodimentsemploying a thermoelectric generator. In one example embodiment, theStirling engine generation system may be positioned in or proximate to abody of water 1050. In other example embodiments, the Stirling enginegeneration system may be geographically separated from the body of water1050, and optionally be in thermal communication therewith, for example,by a secondary pipe system, as illustrated in FIG. 7.

The pipe system 1020 interfaces with a hot junction (also referred to asa hot heat exchanger) of the Stirling engine generator, so as to providethermal communication between the heat transfer medium within the pipesystem 1020 and the hot chamber (also referred to herein as the “hotjunction” or the “hot heat exchanger”). In a manner similar to thatdescribed above with reference to FIGS. 4-8, the heat transfer medium(for example a fluid such as water) is pumped from the pump station 1010down the pipe system 1020 for heating. The transfer medium within thepipe system 1020 is heated by the earth as it descends from the pumpstation towards the bottom of the hole 1040. The heat transfer mediummay be heated to approach the temperature of the earth in the hole 1040.In an exemplary embodiment, the heat transfer medium may be heated inexcess of 200 degrees Fahrenheit. After reaching the lowest point of thepipe system 1020, the heated medium then ascends out of the hole 1040and toward the hot chamber of the Stirling engine generator 1030.

The heated medium within the pipes provides a high temperature sourcefor thermally interfacing with the hot heat exchanger of the Stirlingengine generator 1030. Accordingly, the heat available within the deepwell or hole 1040 provides a very high temperature source in thermalcommunication with the Stirling engine for heating the gas therein. Theheat transfer medium may include any fluid that is capable of beingheated by the earth and capable of retaining a substantial portion ofthe heat for delivery to the hot chamber of the Stirling enginegenerator 1030. In an exemplary embodiment, the fluid is water, however,other fluids may be employed to reduce corrosion and to allow heatingwell above the boiling point of water.

The cold heat exchanger or the cold chamber (also referred to herein asthe “cold junction” or the “cold heat exchanger”) of the Stirling enginegenerator may be in thermal communication with a low temperature source,such as a body of water as further described above with reference toFIGS. 4-8. In an exemplary embodiment of the Stirling engine generator,the cold chamber of the generator is in thermal communication with thebody of water at a point beneath the thermocline of the body of water sothat the cold chamber may access the low temperature water below thethermocline or cool water from the thermocline may be pumped to thesurface to provide a lower temperature heat sink.

In an exemplary embodiment, the high temperature source may be between100 degrees Fahrenheit and 600 degrees Fahrenheit and the lowtemperature source may be approximately 32 and 130 degrees Fahrenheit.It is appreciated, however, that the high temperature source and lowtemperature source are not limited to these temperature ranges but maybe any appropriate temperature ranges. The temperature gradient (ΔT)between the hot junction and the cold junction may be betweenapproximately 470 degrees and approximately 68 degrees in an exemplaryembodiment. Again, it is appreciated, however, that the temperaturegradient is not limited to this range but may be any temperaturegradient. Thus, the use of the heat energy available from within theearth's crust to increase the temperature at the hot heat exchanger ofthe Stirling engine generator and the cold-ness of the water to cool thetemperature of the cold heat exchanger, creating a more powerful heatsink for dissipating heat from the engine, maximizes the temperaturegradient and produces significant amounts of electrical power. Theelectrical power may be created as a direct current. The direct currentmay be transformed to an alternating current. A three-phase current mayalso be created. The electricity generated from the Stirling enginegenerator may be transmitted through power lines to any destination. Inan exemplary embodiment, existing power transfer facilities and powerconduction lines may provide power to any current or newly createdelectrical grid network.

As stated previously, other power generation means that gain advantagewith larger temperature differentials may be used in concert with theheat energy transferred from the earth's crust by the systems andmethods described herein. In one example, a Rankine engine may be usedin much the same manner as either the thermoelectric generator or theStirling engine, cycling the heat transfer medium from the pump stationto the bottom of the well or hole, then through the Rankine engine andback, while also leveraging a low temperature source such as a body ofwater.

FIG. 11 illustrates another example embodiment, including a powergenerating means 1110, which may include a turbine 1112 and generator1114, a pump station 1120, and a pipe system 1130 extending into a deepwell or hole 1140 within the earth's crust, as described in detail withreference to FIGS. 4-10. As illustrated in FIG. 11, the pipe system mayinclude an inner pipe 1132 and an exterior pipe 1134, as is describedmore fully with reference to FIGS. 6 and 9. However, it is appreciatedthat any of these exemplary embodiments may employ other pipeconfigurations, such as, for example, a substantially U-shaped pipe.

It is further appreciated that the pipe system 1130 may configured as aheat pipe or a thermosiphon, as are known. A heat pipe is a heattransfer mechanism operable to transport significant quantities of heatwith a small temperature gradients. Inside a heat pipe, at or near thehigh temperature source, the heat transfer fluid therein vaporizes andnaturally flows and condenses on or near a lower temperature interfacesuch as at the power generating means 1110. After condensing, the liquidfalls or is moved by capillary action back to the high temperaturesource to evaporate again and repeat the cycle. Accordingly, inembodiments where the pipe system 1130 is configured as a heat pipe,heat from the bottom of a hole 1140 can quickly be transferred to thepower generating means 1110, and the heat extracted and used to powerthe turbine 1112. It is further appreciated that while the heat pipe andthermosiphon are described in reference to FIG. 11, any embodiments mayemploy heat pipe technology to configure some or all of the pipe systemsused therein.

The power generating means 1110 may include a Sumrall energy cycleplant, a Matteran energy cycle plant, a flash power plant, a dry steampower plant, a binary power plant, a flash/binary combined cycle powerplant, and the like, each of which are more fully described withreference to FIG. 11.

In an example embodiment using a Sumrall energy cycle plant as the powergenerating means 1110, the heat transfer medium may be one that isliquid at normal room temperatures, but has a lower boiling point thanwater, allowing it to vaporize at lower temperatures. In the Sumrallenergy cycle, the low boiling point medium is delivered directly downthe pipe system 1130, rather than as a secondary fluid interfacingthrough a heat exchanger with the primary heat transfer medium delivereddown the pipe, as in a binary cycle power plant as is known. Examplemedia for use in the Sumrall energy cycle may include isobutane,cyclopentane, or other materials vaporizing below 100 degrees Celsius.Accordingly, a medium with a lower boiling point has a lower heat ofvaporization and thus can be vaporized directly by the heat reachedwithin the pipe system 1130 at the bottom of the hole or well 1140 andthe vapor transported directly to the turbine 1112 in the powergeneration means 1100 for driving a generator 1114 to produce electricalenergy. After being delivered through the turbine, the low boiling pointmedium is then re-condensed to a liquid and delivered back down the well1140 through the pipe system 1130 for the next vaporization cycle. Thisexample embodiment, which may be referred to as a Sumrall energy cycleplant, may be entirely or substantially closed loop in design, and maynot require a low temperature source as in the other thermoelectricgenerators, heat engines, and the like. Furthermore, this exampleembodiment may not require the use of a pump station, as the heat vaporcan rise through the pipe system naturally and be gravity fed to thehigh temperature source. It is further appreciated that a low boilingpoint fluid may be employed in any of the other configurations,providing a gaseous interface at the hot junction rather than a fluidone.

Using a low flashpoint fluid such as isobutane or cyclopentane in aturbine can result in better performance of the turbine as compared tousing water or steam. Low flashpoint fluids can be used at lowerpressures and lower velocity (as compared to water or steam), whichresult in less wear to blades and metal parts of the turbines and otherequipment. Using low flashpoint fluids allows a higher flow rate, whichallows use of a larger diameter turbine. This will also reduce the speedof the working fluid and can result in less wear and damage to turbinecomponents. Also, low flashpoint fluids are less likely to containentrained liquid which can impinge on turbine blades, casings, and othercomponents, and damage the turbine.

In another example embodiment, the power generating means 1110 may be aMatteran energy cycle power plant. The Matteran energy cycle isgenerally a closed loop energy cycle that does not require the use offluid feed pumps, and requires only low temperature heat source as aresult of its use of a refrigerant instead of water as the heat transfermedium and a condensing mechanism (not shown) to recollect vapor, a heatexchanger (not shown) to heat the condensed material prior to deliveryto the high temperature source for heating, connected through a seriesof controllable valves. Accordingly, with reference to FIG. 11, thepower generating means 1110 may include a Matteran energy cycle plant.Thus, the fluid transfer medium in this example embodiment is arefrigerant as is known. Further, though not shown, the Matteran energycycle plant may include at least one condenser in communication with thefluid return pipe 1134 to condense any remaining vapor to its liquidstate. Further, though also not shown, the Matteran energy cycle plantmay include at least one heat exchanger in communication with the fluidreturn pipe 1134 and downstream the previously described heat exchanger.Further, a valve system as is known may selectably control the fluidfrom the turbine 1112 through the condenser and through the heatexchanger prior to delivery to the bottom of the pipe system 1130 andthe bottom of the hole 1140 for heating. After heating, the fluid, whichmay be substantially vaporized, may be delivered to the turbine 1112 ofthe power generating means 1110 for causing a rotational force thereinand transferring to a generator 1114, as is known. After being deliveredthrough the turbine 1112, utilized heat transfer medium would again bedelivered down the fluid return pipe 1134 for subsequent cycles ofcondensing, heating by the heat exchanger, heating by the hightemperature source, and redelivery to the power generating means 1110.

In yet other embodiments, a dry steam power plant or a flash cycle powerplant may be employed as the power generating means 1110. In the drycycle power plant embodiment steam is delivered from within the well(and in one embodiment is an open loop configuration delivering steamexisting within the earth's crust) to a turbine 1112 for powergeneration. In the flash steam power plant, heated water is deliveredfrom within the well (which may include a closed loop configuration asdescribed above with reference to FIGS. 4-10 or an open loopconfiguration) to an additional flash tank (not shown) for creatingsteam prior to deliver to the turbine 1112. Similarly, a binary powerplant or a combination flash/binary combined cycle plant, may employ asecondary working fluid in thermal communication with the pipe system1130, which is then vaporized to drive a turbine 1112 and generator1114. Heat may be transferred from a primary medium being pumped to andfrom the bottom of the well 1140 to the secondary working fluid by wayof a heat exchanger or series of heat exchangers, as are known. The useof an additional working fluid allows having a fluid with differentqualities interfacing with the turbine 1112 than is being pumped downthe pipe system 1130 to the bottom of the well.

It is appreciated that where the term “pump station” is used describingthese example embodiments, the “pump station” need not include an actualpump, as is known, or pumping capabilities. Accordingly, the “pumpstation” as used herein may simply refer to the mechanism operable todeliver the heat transfer medium through the pipe systems to one or bothof the high temperature source and the low temperature source, andreturn to the power generation means, such as the thermoelectricgenerator, the example heat engines, the example turbine generators, andthe like. For example, while any pump means as are known may becontemplated in some example embodiments, other example embodiments maybe gravity fed, siphon-based, displacement-based, and the like.

Geo-thermal generation systems encounter obstacles to efficient orcost-effective power generation. For example, about 40% of allgeo-thermal wells drilled are non-productive, meaning they do not orcannot sustain an economical system for several reasons, including, butnot limited to: insufficient heat resources, insufficient thermalconductivity, insufficient geo-pressure to bring hot brine to thesurface, and others. Furthermore, brine, which is a heat carrier ingeothermal formations can pose significant environmental and operationalconcerns. In traditional geo-thermal processes, the hot brine is pumpedout of the ground from a production well, the heat is extracted aboveground, and the brine is pumped back into the ground. Typical systemsremove about 15-20% of the heat from the brine, and the brine isre-introduced into the geo-thermal formation in an injection well at asignificant distance from the production well, for example, 1-2kilometers or more. Because heat has been removed from the brine, thesaturation conditions of the brine are changed, and precipitation ofbrine components (scaling) on pipe, pump, and heat exchange surfaces canoccur. The precipitation of brine can plug piping, reduce heat transferabilities, increase pumping power requirements, and cause pipe bursting.In order to prevent precipitation of the brine, significant amounts ofwater have to be added back into the brine. The water requirement can beas high as 1,000 acre-feet of water per MW of power produced. Thus, a 50MW geothermal plant may use 16.3 billion gallons of fresh water peryear.

Additionally, brine can contain caustic and toxic components, includingheavy metals such as cadmium, arsenic, selenium, and toxic gasses suchas hydrogen sulfide (H₂S) the like. Moving brine to the surface canresult in the undesirable exposure to and release of these componentsinto the environment. Further, brine is highly corrosive, and the stepsmust be taken to protect against corrosion of the piping systems whichare exposed to the brine.

Embodiments of the current disclosure overcome and/or minimize theproblems of conventional geo-thermal power production. Embodimentsdescribed herein minimize the amount of piping and equipment whichprocesses or is in contact with brine. Embodiments described herein donot pump brine to the surface, but exchange heat in-ground, in thegeo-thermal formation. This eliminates the need for huge amounts ofmake-up water or fresh water. Components of the brine which arehazardous are kept within the geo-thermal formation, rather than beingmoved to the surface. Further systems described below can utilizeexisting, used, or spent oil and gas wells which may not have sufficientgeo-pressure to move the brine to the surface.

The current disclosure relates to geo-thermal power systems whichutilize an in-ground heat exchanger having a primary heat transfer fluidtherein, an above ground heat exchanger in which the primary heattransfer fluid gives up its heat to a secondary heat transfer fluid, anda generating portion which utilizes the secondary heat transfer fluid asthe working fluid. The system can advantageously use an organic Rankinecycle, where an organic liquid (the secondary heat exchange fluid)having a relatively low boiling point such as isobutene, isopentane,cyclopentane, etc., which will undergo a phase change from liquid tovapor in a heat exchanger and then the vapor passes through the turbineand is re-condensed and re-circulated.

FIG. 12A depicts an exemplary embodiment of a system for extracting heatfrom a geothermal feature. A generation system 1200 comprises a primaryheat exchanger portion 1205, a secondary heat exchanger portion 1207,and a generating portion 1208.

The primary heat exchanger portion 1205 includes a hole or well 1240drilled into a geothermal formation 1245 and a primary heat exchanger1220. The well 1240 can be a newly drilled well. The geothermalformation 1245 can have a source of geothermal energy and a heatcarrier, such as a brine within the geothermal formation. In someembodiments, the well 1240 can be a dry well, an expended oil or gaswell, or an unused well. The primary heat exchanger 1220 has a supplyportion 1222 and a return portion 1224 which are inserted into ordisposed within the well 1240 and in the geothermal formation 1245, andwhich are in communication with the secondary heat exchanger portion1207. Portions of the supply portion 1222 and the return portion 1224extend out of the well 1240 to connect to other components of the system1200.

In some embodiments, the temperatures in the well can increase as depthincreases. In some wells, temperature up to 3000 feet can decrease, thatis, get colder. In some embodiments, the temperatures may increase below300 feet, such that useful heat transfer from the geothermal formation1245 can occur. In some embodiments, the geothermal features can haveincreasing temperatures from 3000 feet to 12,000 feet or deeper.Temperatures down hole of 600° F. or higher can be advantageous foroperation of the system 1200. Heat exchange fluid temperatures exitingthe return portion 1224 can advantageously be around 600° F. The primaryheat exchanger 1220 can extend the along the full depth of the well ornearly the full depth of the well, and heat transfer can happen allalong the depth of the well. In some embodiments, the heat exchanger canextend through only the portion of the well having in-groundtemperatures high enough for efficient heat transfer.

The primary heat exchanger 1220 will be described in greater detailbelow. A pump 1210 is in fluid communication with the supply portion1222 and the return portion 1224 and provides a motive force forcirculating a primary heat transfer fluid through the supply portion1222 and the return portion 1224. In some embodiments, the pump 1210 cangenerate a positive pressure to force the primary heat transfer fluiddown the well 1240 within the geothermal formation 1245. In someembodiments, the pump 1210 can provide a negative pressure to draw theprimary heat transfer fluid up out of the well via the return portion1224. This can be advantageous, as the static head of the fluid in thesupply portion 1222 can assist in moving the primary heat transfer fluidout of the well 1240.

The pump 1210 can be a centrifugal pump, a positive displacement pump, asource of pressurized air or an inert gas, or any other type of pump.The pump 1210 can be electrically, mechanically, or fluid driven. Aperson of skill in the art will understand that the pump 1210 can be anycomponent capable of providing a motive force to circulate the primaryheat transfer fluid into and out of the well 1240.

In some embodiments, the primary heat transfer fluid can be a fluidhaving a high heat capacity, such as water. In some embodiments, theprimary heat transfer fluid can be a high temperature vapor/liquid phasefluid or an organic heat transfer fluid. An ultrahigh-temperature heattransfer fluid, such as Therminol®, can be advantageously used. In someembodiments, the primary heat transfer fluid can be a mixture ofTherminol and nano-powder, such as nano-powder magnesium. Using a hightemperature heat transfer fluid such as Therminol® can improve the heatabsorption from the geothermal formation 1245 and reduce corrosion inthe primary heat exchanger 1220 and the secondary heat exchanger 1215,as compared with using water and steam. It is desirable that the heattransfer fluid be capable of handling the high heat associated withgeothermal power generation. The thermal conductivity of the primaryheat transfer fluid can be increased by addition of nano-powders orsimilar components. The primary heat transfer fluid can be a nanofluid.A nanofluid can be a fluid which has nanometer-sized particles of metal,such as magnesium, or ceramic or other particles having an average sizeof 1-100 nm which improve the heat transfer capability of the fluid. Insome embodiments, nano-powder magnesium has a heat capacity of 1047J/kg-K. The heat capacity of the primary heat transfer fluid can beincreased by addition of other additives, such as lithium. In someembodiments, the primary heat exchanger 1220 can be kept pressurized toensure the primary heat transfer fluid is maintained as a liquid toprovide sufficient heat transfer capability and pumpability. In someembodiments, the primary heat transfer fluid can be other materialssuitable for geothermal heat transfer such as eutectic salts, which canimprove the efficiency of the system 1200.

Heat flow in the primary heat exchanger 1220 occurs as the primary heattransfer fluid is pumped down into the well 1240, or is otherwise movedvia a motive force into the well 1240. The heat from the geothermalformation 1245 is carried by the heat carrier or brine to the supplyportion 1222. The heat from the heat carrier or brine is transferredthrough a wall of the supply portion 1222 and into the primary heattransfer fluid. The heat transfer fluid absorbs heat and is moved viamotive force, such as a pump, to the secondary heat exchanger portion1207, where the primary heat transfer fluid gives up its heat to asecondary heat transfer fluid. The cooler primary heat transfer fluid isre-circulated down into the well to repeat the cycle.

The primary heat transfer fluid returning to the well is already heatedabove ambient, because it does not give up all its heat to the secondaryheat transfer fluid. In a typical geothermal operation, only about15-25% of the heat (from the brine or steam) is extracted from the heatsource and the remainder of the brine or steam is reinjected far fromthe point of extraction and therefore is of no further use to theprocess. The current application, however, is designed to allow thisresidual heat (between 75-85% of the original heat) to be reinjectedback into the same well from which it was extracted. In this way, theprimary fluid can be reheated to optimal temperature with less heatinput from the geothermal formation to the desired temperature for theoptimal thermal operation of the system. This results in less wastedheat in the system 1200, and improves efficiency of operation

It will be appreciated, however, that the overall surface area of theprimary heat exchanger 1220 can be increased by increasing the pipediameters as much as possible. In some embodiments, such as, forexample, when using an existing well, the diameter of the existing well1240 may only allow for a heat exchanger that has a smaller diameterthan the existing casing. However, by employing of an under reamer theopen hole section of the well, that is, sections of the well which donot have a casing, can be increased in diameter (beyond that of theexisting casing) and an expandable casing or support collars asdescribed elsewhere herein may be inserted into the open hole section ofthe well, thus providing a larger diameter primary heat exchanger 1220.

The secondary heat exchanger portion 1207 comprises a secondary heatexchanger 1215, a hot fluid line 1232, and a cold fluid line 1234. Insome embodiments, the secondary heat exchanger 1215 can be a shell andtube type heat exchanger. In some embodiments, the supply portion 1222and the return portion 1224 are in fluid communication with a tubeportion the secondary heat exchanger 1215. The hot fluid line 1237 andthe cold fluid line 1234 are in fluid communication with a shell portionthe secondary heat exchanger 1215. The primary heat transfer fluid flowsthrough the tube portion of the secondary heat exchanger 1215 and givesup its heat to a secondary heat transfer fluid in the secondary heatexchanger 1215, which flows on the shell side of the secondary heatexchanger 1215. The secondary heat transfer fluid is vaporized by theheat of the primary heat transfer fluid, and the vaporized secondaryheat transfer fluid flows into the generator portion 1208.

The secondary heat transfer fluid is circulated through the hot fluidline 1232 and the cold fluid line 1234 via a feed pump 1237. The feedpump 1237 can be any type of pump capable to deliver a motive force tocirculate the secondary heat transfer fluid into the secondary heatexchanger 1215, and can be similar to pumps described elsewhere herein.

In some embodiments the primary and secondary heat transfer fluids donot mix and are isolated from one another in the secondary heatexchanger 1215.

The secondary heat transfer fluid can be a fluid which vaporizes at thetemperatures achieved within the secondary heat exchanger 1215. In someembodiments, the secondary heat transfer fluid can be water. In someembodiments, the secondary heat transfer fluid can advantageously be anorganic compound having a flashpoint lower than that of water. In someembodiments, the secondary heat transfer fluid can advantageously beisobutane or cyclopentane.

The generator portion 1208 includes a turbine 1230, a generator 1232 anda condenser 1235. The vaporized secondary heat transfer fluid impingesblades of the turbine 1230, which spins a turbine shaft which ismechanically connected to the generator 1232. As the turbine 1230 spins,the generator 1232 generates electricity. The turbine 1230 canadvantageously be part of an organic Rankine cycle.

The condenser 1235 operates to condense the secondary heat transferfluid using a coolant supplied from a cooler 1238. The cooler 1238 caninclude one or more water or air cooled towers as are known in the art.In some embodiments, the cooler 1238 can be a large heat sink, such as abody of water, and coolant can be pumped via a pump (not shown) ornaturally circulated through the condenser 1235, similar to heat sinksdescribed elsewhere herein. The condensed secondary heat transfer fluidis circulated into the secondary heat exchanger 1215 via the feed pump1237, where it is heated and vaporized again.

The heat exchangers 1215 and 1235 are described herein as shell-and-tubetype heat exchangers. However, one of skill in the art will understand,guided by this disclosure, that any type of heat exchanger can be used.Additionally, a person of skill in the art will understand that thefluids flowing in the shell and tube sides of the heat exchangers can bechanged without departing from the scope of this disclosure.

In some embodiments, the generation system 1200 may not include asecondary heat exchanger 1215. In this case, the primary heat transferfluid is heated in the well 1240, circulates to the turbine 1230 as theworking fluid for the turbine 1230, and is then condensed in thecondenser 1235 to return to the well 1240.

FIG. 12B depicts a close-up cross-sectional view of a portion of theprimary heat exchanger 1220 within the well 1240. The well 1240 can be abore formed within the geothermal formation and can be similar to thatdescribed elsewhere herein. Within the geothermal formation 1245, aliquid, such as a brine, can be present. The brine is heated within thegeothermal formation 1245 by geological effects. The heated brine flowswithin geothermal formation 1245 and within the well 1240 and suppliesheat to the heat exchanger 1220. It will be appreciated, that in hot/drydown hole conditions, such as where there is no brine) that heat may betransferred by the thermal conductivity of the surrounding rock and thata high temperature and highly thermally conductive material may beinserted between the exterior of the heat exchanger and the wall of thedry well to enhance thermal conductivity under hot/dry downholeconditions. In this case, the highly thermally conductive material canbe the heat carrier to transfer heat from the hot rock to the primaryheat exchanger 1220.

The primary heat exchanger 1220 comprises the supply portion 1222 andthe return portion 1224. The supply portion 1222 is bounded by an outershell 1264, which is in contact with the geothermal formation 1245, andby the return portion 1224. The outer shell 1264 comprises a pluralityof casing units or segments which are connected to each other, end toend, using casing joints or casing couplers 1227. In this way, the outershell 1264 can be as long as necessary to reach the depth of thegeothermal formation 1245. The casing couplers 1227 connect one sectionof casing to another, and form the external boundary of the primary heatexchanger 1220.

The outer shell 1264 can be a casing in an expended or unused oil or gaswell. In some embodiments, the outer shell 1264 can be provided orpositioned within a drilled well which doesn't already have a casing. Inthe case where a pre-existing casing exists in a well, the primary heatexchanger 1220 can be formed by inserting the return portion 1224 withinthe casing and being sealed to prevent in-leakage of brine orout-leakage of primary heat transfer fluid. The return portion 1224 canbe supported within the casing, or supply portion 1222 as describedherein.

As noted above, brine is highly corrosive and susceptible toprecipitation or scaling on the outer shell 1264 of the supply portion1222. Scale material, such as iron silicate or barium sulfate candeposit or build-up on the well side surface of the outer shell 1264.Calcium carbonate might not scale on the outer shell 1264 because theheat transfer process in the well 1249 is isobaric. Scale build-up onthe outer shell 1264 reduces the thermal conductivity of the outer shell1264 which lowers the amount of heat transferred from the brine to theprimary heat transfer fluid.

To prevent or minimize corrosion and scale build-up and to prolong theuseful operational life of the primary heat exchanger, the materials ofthe outer shell 1264 can be carefully selected. For example, the outershell can be formed out of stainless steel which is then clad with acorrosion resistant material, such as nickel alloy 625. The nickel alloy625 resists corrosion and scaling, and maintains a high thermalconductivity of the outer shell 1264. Corrosion resistant materials canalso be effective scale inhibitors, because the corrosion resistantmaterials resist formation of nucleation sites which are required forscale to begin forming.

Also, the outer surface of the outer shell 1264, which is in contactwith the brine during operation, can be coated with a non-metallicmaterial which is very smooth. A coating using a non-metal material,such as carbon or boron. This non-metal material can be applied viachemical vapor deposition (CVD) or vapor deposition alloying (VDA). Thenon-metal material prevents an ionic bonding site from forming, thuspreventing scale formation.

A diamond-like carbon (DLC) coating can be advantageously applied to theouter surface of the outer shell 1264. A DLC is a class of amorphouscarbon material that has significant amounts of sp³ hybridized carbonatoms. One form of DLC, for example, tetrahedral amorphous carbon (ta-C)can be advantageously used. A 2 mm thick coating of ta-C can increasegreatly the resistance of stainless steel (or lower or higher grades ofsteel) to abrasion, scaling, and other fouling. Other forms of DLC canalso be advantageously used, such as forms having hydrogen, graphiticcarbon, or metals can be used to reduce expenses and to impart otherdesirable properties. In some embodiments, carbon nitride, boronnitride, or other carbon- or boron-containing materials can beadvantageous applied to the outer surface of the outer shell 1264 toprevent or minimize scaling and corrosion. A boron nitride coating(applied via CVD or VDA or similar method) can improve the operationallifetime of the primary heat exchanger 1220 by up ten times.

In some embodiments, the outer shell 1264 can be formed of or coatedwith highly thermally conductive ceramics, which resist scaling andcorrosion from brine.

The return portion 1224 includes a return pipe 1254 that isconcentrically disposed within the outer shell 1264 of the supplyportion 1222. The flow velocity through the return portion 1254 will behigher than that in the supply portion 1222, because the return pipe1254 has a smaller diameter than the outer shell 1264. The highervelocity in the return pipe 1254 can limit heat loss through the wallsof the return pipe to the cooler portion of the primary heat transferfluid in the supply portion 1222, as the primary heat transfer fluidmoves up the return pipe 1254.

Additionally, to minimize the heat transfer between the supply portion1222 to the return portion, through the return pipe 1254, a thermalinsulation layer 1225 can be added to a surface of the return pipe 1254.This insulation layer can prevent, lower, and/or minimize unwanted heattransfer between the supply portion 1222 and the return portion 1224.The thermal insulation layer 1225 can be disposed on an inner surface,on an outer surface, or on both inner and outer surfaces of the returnpipe 1254. In some embodiments, the thermal insulation layer cancomprise a thermally resistant polymer, such as, for example,polybenzimidazole (PBI) or other similar material which has a highthermal resistance and low thermal conductivity.

In some embodiments, the return pipe 1254 can be vacuum insulatedtubing. The vacuum insulated tubing is a dual walled tube having anevacuated space between the two walls. The evacuated space insulates theprimary heat transfer fluid in the return pipe 1254 from the primaryheat transfer fluid in the supply portion 1222. In some embodiments, thereturn pipe can be vacuum insulated tubing and additionally have aninsulating coating thereon.

The return pipe 1254 is supported in place concentrically within theouter shell 1264 using one or more centralizers 1228. The centralizersare angled braces which extend from the inner surface of the outer shell1264 at or near casing couplers 1227, and which are connected to theouter surface of the return pipe 1254. The centralizers 1228 are angleddownward from the inner surface of the outer shell 1264 toward the outersurface of the return pipe 1254. Although FIG. 12B only depictscentralizers 1228 on one side of the primary heat exchanger 1224, theymay extend around the circumference of the return pipe 1254 as will bedescribed with regard to FIG. 12D. The centralizers 1228 act to supportand maintain the return pipe 1254 centered within the outer shell 1264.The centralizers 1228 have a narrow profile to minimize hydraulicresistance to flow of the primary heat transfer fluid.

The return pipe 1254 is formed having one or more perforations 1223therein. The one or more perforations 1223 provide a fluid path betweenthe supply portion 1222 and the return portion 1224. In someembodiments, the return pipe 1254 is capped on a lower surface 1255, andthe perforations are formed circumferentially proximate the bottomsurface 1255 of the return pipe 1254. In some embodiments, the lowersurface 1255 of the return pipe 1254 is not capped and heated primaryheat transfer fluid flows up into the bottom of the return pipe 1254. Insome embodiments, the return pipe 1254 includes perforations 1223 and isuncapped on the lower surface 1255.

The perforations 1223 can advantageously provide for an improvement inpower requirements to circulate the first heat transfer fluid throughthe primary heat exchanger 1220 by decreasing the pressure on the bottompart of the shell as a result of pumping action.

The primary heat transfer fluid flows through the primary heat exchanger1220 in the directions indicated by arrows 1222 a and 1222 b. Toillustrate, cold, or relatively colder primary heat transfer fluid flowsfrom the secondary heat exchanger 1215 down the well 1240 in the supplyportion 1222, around the centralizers 1228, and to or near the bottomsurface 1255 of the primary heat exchanger 1220, as shown by arrows 1222a. As the primary heat transfer fluid flows down the supply portion1222, it picks up heat from the geothermal formation 1245 via the outershell 1264 which is in thermal connection with the brine. The heat fromthe geothermal formation conducts through the outer shell 1264 andconducts and/or convects into the primary heat transfer fluid.

The hot, or relatively hotter primary heat transfer fluid flows throughthe perforations 1223 and into the return pipe 1254. The insulation onthe return pipe minimizes heat transfer between the hot primary heattransfer fluid in the return pipe 1254 and the colder primary heattransfer fluid flowing down in the supply portion 1222. The hot primaryheat transfer fluid then flows up the return pipe 1254 and to thesecondary heat exchanger 1215 or, in some embodiments, to the turbine1230.

The outer shell 1264 of the primary heat exchanger 1220 is supported inplace within the well 1240. The outer shell 1264 generally has a smallerdiameter than the well 1240, such that there is a gap between the outershell 1264 and the inner wall 1263 of the well 1240.

In some used or dry oil and gas wells, portland cement or a high silicacement has been used to support a casing within the well 1240. In someembodiments described herein, the casing can form the outer shell 1264of the primary heat exchanger 1220. Portland cement and other similarstructural materials used in wells have a very low thermal conductivity.Portland cement, specifically, has a thermal conductivity of about 0.2W/m·K. It has been found that using a support material having a lowthermal conductivity greatly inhibits heat transfer in a well 1240. Astructural material supporting the primary heat exchanger 1220 havingsuch a low thermal conductivity would greatly inhibit heat transfer fromthe geothermal formation 1245 and the brine to the primary heatexchanger 1220. When using an existing well, such as a dry oil or gaswell a portion of the existing well will already be cased and cementedwith low conductivity cement until the casing is well within thegeothermal formation so that geothermal brine cannot flow back up andinto the much more-shallow fresh water aquifers. Below a certain depth,in some embodiments, the bottom ⅔ of the depth of the well) there isopen hole, or non-cased, well, which is at a very high temperaturewithin the geothermal formation 1245, and into which the heat exchangermay be inserted and where the heat transfer operations described hereincan be performed. In one example, in a 12,000 ft. deep well, for thefirst three thousand feet, the subsurface temperature is cooler than thereturning primary heat transfer fluid temperature (355° F.), therefore,the non-conductive cement prevents heat loss to the upper formationduring its initial return cycle, and the only section which is not beingtaken advantage is the depth between 3,000 and 4,000 ft. (where the wellis open to the geothermal formation).

It has been found that preferred thermal conductivity values for astructural material for supporting the primary heat exchanger 1220within the well 1240 are around 15 W/m·K. A lower thermal conductivitythan 15 W/m·K may not provide sufficient heat flux to efficiently use orto maximize use of the geothermal energy, and thermal conductivityvalues more than 15 W/m·K further increase heat flux, but to a point ofdiminishing returns for the cost of providing materials with the higherthermal conductivity. A cement or structural material having highthermal conductivity can advantageously be used to support a casing orthe outer shell 1264 within the well 1240. In some embodiments, as willbe described in greater detail below, the primary heat exchanger 1220can be suspended or supported within the well 1240 without using acement, concrete or grout.

To achieve a preferred or higher thermal conductivity in the supportmaterial a concrete or grout having thermally enhanced materials can beused. For example, a cement or grout can be thermally enhanced by addingmetallic powders, such as aluminum, copper, magnetite, etc. Adding thesematerials to the cement or grout, which have high thermal conductivityvalues, increases the thermal conductivity of the resulting concrete.The cement or grout should have a neutral or close to neutral pH so asnot to react with the added metallic powders. An alkaline or acidicgrout could react with the added metallic materials and which couldresult in generation of gas, corrosion, and weakening of the cement orgrout.

In some embodiments, such as depicted in FIG. 12B, the outer shell 1264is supported in place by using a thermally enhanced cement 1260. Thethermally enhanced cement 1260 can be disposed between the outer shell1264 and the inner wall 1263 of the well 1240. The thermally enhancedcement 1260 improves heat transfer between the geothermal formation 1245and the primary heat exchanger 1220, and supports the outer shell 1264in place within the well 1240.

FIG. 12C depicts an embodiment of the primary heat exchanger 1220 withinthe well 1240, where the outer shell 1264 is supported in place using aplurality of lateral support collars 1261. The lateral support collars1261 extend from the inner wall 1263 of the well 1240 and contact theouter shell 1264. The lateral support collars 1261 can be spaced aroundthe circumference of the outer shell 1264 and along a length of theouter shell 1264, and can extend at an angle downward from the outershell 1264 toward the inner surface 1263 of the well 1240. Thus, usinglateral support collars 1261 leaves a gap 1246 between the inner wall1263 of the well 1240 and the outer shell 1264. The brine in thegeothermal formation can flow around and through the gap 1246, and thebrine can directly contact the outer shell 1264 of the primary heatexchanger 1220. This arrangement increases the heat transfer from thegeothermal formation to the primary heat exchanger 1220. It will beunderstood that in some wells 1240 there may be fresh groundwater orother heat transfer medium other than brine in contact with the outershell 1264.

Having the lateral support collars 1261 extend radially outward and downfrom the outer shell 1264 also provides support for, or limits movementof, the primary heat exchanger downward into the well 1240, or in thenegative y-axis direction, but allows for movement upward, out of thewell 1240, or in the positive y-axis direction. The lateral supportcollars 1261 can be attached to the outer surface of the outer shell1264 at a junction which is moveable, or hinges. Before the heatexchanger 1220 is inserted into the well, the lateral support collarscan be fastened at a first end to the outer shell of the heat exchangervia a biased and hinged, pivotable, or moveable, but not removable,junction. The other end of the lateral support collars can be foldeddown against the outer surface of the outer shell 1264, and can be heldin place by a temporary connection or a degradable material. As the heatexchanger 1220 is inserted into the well 1240, the lateral supportcollars are flush or nearly flush with the outer surface of the outershell 1264, and the heat exchanger 1220 can extend into the well 1240without interference from the lateral support collars 1261. When theheat exchanger is in place in the well 1240, the temporary connection ordegradable material can degrade. When the temporary connection degrades,a bias force in the junction at the first end of the lateral supportcollars 1261 causes the lateral support collars 1261 to extend to theposition shown in FIG. 12C, and impinge the inner surface of the well1240, supporting the heat exchanger 1220 within the well 1240.

In some embodiments, the temporary connection or degradable material isconfigured to degrade due to caustic conditions in the well 1240, or tothermally degrade due to the high temperatures down the well 1240, orboth. Another degradation mechanism can be used as well.

This arrangement allows the primary heat exchanger 1220 to be easilyremoved upward out of the well 1240 if necessary, but prevents theprimary heat exchanger 1220 from moving farther downward into the well1240. In some embodiments, the primary heat exchanger 1220 canadvantageously be suspended into the well 1240 from the land or watersurface.

FIG. 12 C also depicts the centralizers 1228 as horizontal braces whichare connected to the return pipe 1254 at a junction 1229, and which arenot connected to the outer shell 1264. This arrangement centers thereturn pipe 1254 within the shell 1264, and enables the return pipe 1254to be removed from the shell 1264 (or the casing) or the well 1240 formaintenance, replacement, inspection, and the like. As the return pipe1254 is removed from the casing, the centralizers 1228 are removed withthe return pipe 1254. This arrangement also allows for insertion of thereturn pipe 1254 into the shell 1264 without having to navigate an arrayof structures connected to the shell 1264.

In some embodiments, the centralizers 1228 can be horizontally arrangedand connected to both the return pipe 1254 and the shell 1264.

Although the angled centralizer 1228 arrangement in FIG. 12B is shown inan embodiment having thermally enhanced concrete 1260 and the horizontalcentralizer 1228 arrangement in FIG. 12C is shown in an embodiment withsupport collars 1261, it is explicitly contemplated that horizontalcentralizers 1228 can be used in heat exchangers supported by thermallyenhanced concrete 1260 and that angled centralizers can be used in heatexchangers supported by support collars 1261.

FIG. 12D is a top view of the primary heat exchanger 1220 illustratingthe arrangement of the centralizers 1228. As shown, the centralizersextend radially outward from the return pipe 1254 and toward the outershell 1264, and are disposed circumferentially around the return pipe1254. There is space between the centralizers 1228 to allow for the flowof primary heat transfer fluid. The view of centralizers 1228 shown inFIG. 12D can apply for either angled or horizontal centralizers 1228.FIG. 12D depicts that the centralizers 1228 will be narrow to minimizehydraulic resistance to flow of the first heat transfer fluid.

The systems and methods for generating electricity can also be adaptedfor heating and cooling of facilities, equipment, and the like. Inheating and cooling applications, the system need not include a turbineor a generator, but can use heat exchangers and control systems toprovide temperature control of a building, room, equipment and the like.Additionally using absorption or adsorption chillers can advantageouslyprovide cooling for facilities and equipment using geothermal energydescribed herein or can be used for the condensation of atmosphericwater vapor.

The generation systems and details regarding the primary heat exchangerdescribed with regard to FIG. 12 can be advantageously used inembodiments having a thermoelectric generator, a Stirling engine, aMatteran cycle, organic Rankine cycle, traditional Rankine cycle, or anyother cycle or process described herein.

In some embodiments, for example, where a well has insufficientgeothermal pressure or the heat carrier movement within the geothermalformation is lower than desired, steps can be taken to ensure that thereis sufficient heat carrier flow within the geothermal formation and thewell. For example, hydraulic fracturing can be performed in the areanear the well to increase the overall volumetric exposure of the heatcarrier to the geothermal formation, and by creating circulationpathways around, over, and on the primary heat exchanger. In someembodiments, the hydraulic fractures can be performed using sand with anaverage particle diameter of about 80 mesh or 177 micrometers, forexample included in the fracturing water. A person of skill in the art,guided by this disclosure, will understand how other sand diameters canbe used in the embodiments described herein. In some embodiments, thesand can be coated or mixed with scale inhibiting chemicals. Thescale-inhibiting chemicals can be inserted into the hydraulic fractureto prevent scale formation on the outer shell of the primary heatexchanger. Such chemicals can include acrylic acid polymers, maleic acidpolymers and phosphonates. In some embodiments, the scale-inhibitingchemicals can be chosen for their desirable solubility, thermalstability, and dosage efficiency characteristics.

Construction of a well can be accomplished by inserting a plurality ofsupport collars as described herein into a drilled well in a geothermalfeature. Casing units, or casing segments can be assembled on thesurface and then inserted into the well and supported in place by thesupport collars. In some embodiments, casing segments are individuallyinserted into the well and are supported by the support collars. Whenthe casing portion is complete, a return pipe can be inserted co-axiallyinto the casing, appropriate inlets and outlets and connections can bemade. In some embodiments, the heat exchanger can be inserted into thewell as a complete unit, and can be supported by the support collars.When the heat exchanger has scaled or is unable to provide efficientheat transfer, the unit can be removed from the well and replaced with anew heat exchanger or the removed heat exchanger can be cleaned/repairedand reinserted into the well.

It should be apparent that the foregoing relates only to exemplaryembodiments of the invention and that numerous changes and modificationsmay be made herein without departing from the spirit and scope of theapplication as defined herein.

The above description discloses several methods and materials of thepresent invention. This invention is susceptible to modifications in themethods and materials, as well as alterations in the fabrication methodsand equipment. Such modifications will become apparent to those skilledin the art from a consideration of this disclosure or practice of theinvention disclosed herein. Consequently, it is not intended that thescope of the present invention be limited to the specific embodimentsdisclosed herein, but that it cover all modifications and alternativescoming within the true scope and spirit of the invention.

The foregoing description details certain embodiments of the systems,devices, and methods disclosed herein. It will be appreciated, however,that no matter how detailed the foregoing appears in text, the systems,devices, and methods can be practiced in many ways. As is also statedabove, it should be noted that the use of particular terminology whendescribing certain features or aspects of the invention should not betaken to imply that the terminology is being re-defined herein to berestricted to including any specific characteristics of the features oraspects of the technology with which that terminology is associated.

It will be appreciated by those skilled in the art that variousmodifications and changes may be made without departing from the scopeof the described technology. Such modifications and changes are intendedto fall within the scope of the embodiments. It will also be appreciatedby those of skill in the art that parts included in one embodiment areinterchangeable with other embodiments; one or more parts from adepicted embodiment can be included with other depicted embodiments inany combination. For example, any of the various components describedherein and/or depicted in the Figures may be combined, interchanged orexcluded from other embodiments.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations.

In addition, even if a specific number of an introduced claim recitationis explicitly recited, those skilled in the art will recognize that suchrecitation should typically be interpreted to mean at least the recitednumber (e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

The term “comprising” as used herein is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps.

What is claimed is:
 1. A geothermal energy system comprising: a primaryheat exchanger positioned within a well, the well in contact with ageothermal formation and a heat carrier within the geothermal formation,the primary heat exchanger containing a first heat transfer fluidconfigured to absorb heat from the heat carrier in the primary heatexchanger, wherein the primary heat exchanger is supported within thewell by a plurality of support collars, each of the plurality of supportcollars comprising a first and second end, wherein the first ends of theplurality of support collars are securely connected to an inner wall ofthe well, and wherein the second ends of the plurality of supportcollars contact an outer surface of a shell of the primary heatexchanger at a point higher in the well than the corresponding firstends of the plurality of support collars; a secondary heat exchanger inthermal communication with the primary heat exchanger, the secondaryheat exchanger containing a second heat transfer fluid, wherein thefirst heat transfer fluid and the second heat transfer fluid aremaintained separate from each other, and wherein the second heattransfer fluid has a flash point below that of water; and a turbine influid communication with the secondary heat exchanger, wherein thesecond heat transfer fluid is vaporized in the secondary heat exchangerand the vaporized second heat transfer fluid is the working fluid in theturbine; and a generator connected to the turbine, the generatorconfigured to generate electricity based on movement of the turbine. 2.The geothermal energy system of claim 1, wherein the primary heatexchanger comprises a supply portion and a return portion, the supplyportion comprising the shell in thermal communication with thegeothermal formation, and wherein the return portion is concentricallylocated within the shell of the supply portion.
 3. The geothermal energysystem of claim 2, wherein the return portion comprises a thermallyinsulated pipe, wherein the thermally insulated pipe is configured toinsulate the hot first heat transfer fluid in the return portion fromthe relatively colder first heat transfer fluid in the supply portion ofthe primary heat exchanger.
 4. The geothermal energy system of claim 3,wherein the thermally insulated pipe is suspended within the shell ofthe primary heat exchanger via a plurality of centralizers, thecentralizers positioned within the shell of the primary heat exchangersuch that the primary heat exchange fluid is in contact with theplurality of centralizers.
 5. The geothermal energy system of claim 4,wherein the plurality of centralizers are connected to an outer surfaceof the thermally insulated pipe and are not connected to an innersurface of the shell.
 6. The geothermal energy system of claim 3,wherein the thermally insulated pipe has a first end located near abottom portion of the shell of the supply portion and a second endconnected to the secondary heat exchanger, and wherein the first end ofthe thermally insulated pipe is closed and comprises a plurality ofperforations therein to allow the first heat transfer fluid to flow fromthe supply portion into the thermally insulated pipe.
 7. The geothermalenergy system of claim 1, wherein the shell comprises a well casing, thecasing comprising a plurality of casing segments positioned within thewell.
 8. The geothermal energy system of claim 7, wherein a plurality ofcentralizers are connected to an inner surface of the casing atjunctions between the casing segments.
 9. The geothermal energy systemof claim 1, wherein the primary heat exchanger is supported within thewell by a cement or grout having high thermal conductivity.
 10. Thegeothermal energy system of claim 1, wherein the primary heat exchangeris suspended at or near the surface of the earth or the sea floor. 11.The geothermal energy system of claim 1, wherein the heat carriercomprises a thermally conductive material inserted between the outersurface of the primary heat exchanger and the inner wall of the well.12. The geothermal energy system of claim 1, wherein the heat carrier isa brine flowable within the geothermal formation.
 13. The geothermalenergy system of claim 1, wherein the plurality of support collarssupport the shell of the primary heat exchanger at a position above thebottom of the well.
 14. The geothermal energy system of claim 1, whereinthe plurality of support collars are positioned within the well suchthat the plurality of support collars are in contact with the heatcarrier in the geothermal formation, and the heat carrier is able toflow around the plurality of support collars to contact the primary heatexchanger.
 15. The geothermal energy system of claim 1, wherein theshell comprises an anti-scaling coating on a well-facing surface of theshell, the coating comprising a very smooth non-metallic material whichprevents an ionic bonding site from forming, thus preventing scaleformation and also inhibiting corrosion.
 16. The geothermal energysystem of claim 1, wherein the shell comprises an anti-scaling coatingon a well-facing surface of the shell, the coating comprising carbon orboron applied via chemical vapor deposition or vapor depositionalloying.
 17. The geothermal energy system of claim 1, wherein the shellcomprises an anti-scaling coating on a well-facing surface of the shell,the coating comprising an amorphous carbon material that has significantamounts of sp³ hybridized carbon to retard both corrosion and scaling.18. The geothermal energy system of claim 1, wherein the shell comprisesan anti-scaling coating on a well-facing surface of the shell, thecoating comprising carbon nitride or boron nitride, to prevent orminimize scaling and corrosion.
 19. The geothermal energy system ofclaim 1, wherein the shell comprises an anti-scaling coating on awell-facing surface of the shell, the coating comprising highlythermally conductive ceramics which resist scaling and corrosion.
 20. Amethod of generating electricity using geothermal energy comprising:moving a first heat transfer fluid into a primary heat exchangerpositioned within a well, the well in contact with a geothermalformation and a heat carrier within the geothermal formation and theprimary heat exchanger is supported within the well via a plurality ofsupport collars, each of the plurality of support collars comprising afirst and second end, wherein the first ends of the plurality of supportcollars are securely connected to an inner wall of the well, and whereinthe second ends of the plurality of support collars contact an outershell of the primary heat exchanger at a point higher in the well thanthe corresponding first ends of the plurality of support collars;absorbing, in the first heat transfer fluid, heat from the heat carrierin the well; moving the first heat transfer fluid out of the primaryheat exchanger and out of the well and into a secondary heat exchanger;transferring heat from the first heat transfer fluid to a second heattransfer fluid within the secondary heat exchanger, vaporizing thesecond heat transfer fluid in the secondary heat exchanger; flowing thevaporized secondary heat transfer fluid into a turbine, the turbineconnected to an electrical generator and the vaporized secondary heattransfer fluid moving the turbine; and generating electricity in theelectrical generator using the movement of the turbine.
 21. The methodof claim 20, wherein moving the first heat transfer fluid into theprimary heat exchanger comprises: moving the first heat transfer fluiddown a supply portion of the primary heat exchanger; and contacting,with the first heat transfer fluid, the shell of the primary heatexchanger and a surface of a return pipe disposed concentrically withinthe shell of the primary heat exchanger.
 22. The method of claim 20,wherein moving the first heat transfer fluid out of the primary heatexchanger and out of the well comprises flowing the first heat transferfluid through a return pipe disposed concentrically within the shell ofa supply portion of the primary heat exchanger, wherein the return pipeis thermally insulated to minimize heat transfer between the primaryheat transfer fluid within the return pipe and the primary heat transferfluid in the supply portion of the primary heat exchanger.
 23. Themethod of claim 20, further comprising flowing the heat carrier betweenthe inner wall of the well and the outer shell of the primary heatexchanger, and around the plurality of support collars.
 24. The methodof claim 20, further comprising: inserting the primary heat exchangerinto the well, the primary heat exchanger having the plurality ofsupport collars attached thereto, the second end of each of theplurality of support collars being moveably attached to an outer surfaceof the primary heat exchanger, and the first end of each of theplurality of support collars being temporarily connected to the outersurface of the primary heat exchanger via a degrading connection; anddegrading the degrading connection such that the first end of each ofthe plurality of support collars extends to contact the inner wall ofthe well.
 25. The method of claim 20, wherein the well comprises acasing extending only along a portion of the well, the method furthercomprising: drilling, using an under reamer, a portion of the well wherethe casing does not extend to increase the diameter of the well; andpositioning the primary heat exchanger in the portion of the well havingthe increased diameter.
 26. A heat exchanger for use in a geothermalapplication comprising: a casing disposed within a well, having ananti-scaling and/or anti-corrosion layer thereon configured to contain aheat transfer fluid, the casing forming a shell; a plurality of supportcollars disposed within the well, the plurality of support collarssupporting the casing within the well, the plurality of support collarsdisposed at a generally upward angle from an inner surface of the welltoward the casing; a return pipe disposed co-axially within the shell,wherein the arrangement of the casing and the return pipe form anannulus between the return pipe and the shell, the inner volume of thereturn pipe being thermally insulated from the annulus; a plurality ofcentralizers disposed within the annulus, each of the plurality ofcentralizers comprising a first end and a second end, the first end ofthe plurality of centralizers connected to an inner surface of the shelland the second ends of the plurality of centralizers connected to anouter surface of the return pipe, the centralizers having a low profileto minimize hydraulic resistance to flow within the annulus; and whereinthe plurality of support collars are configured to allow flow of a heatcarrier between the inner surface of the well and the casing.